The present invention relates to improvements in semiconductor devices and, more particularly, to arrangements for preventing leakage paths from forming between metal electrodes or the like and for preventing deterioration in the characteristics and corrosion of semiconductor device.
In the fabrication of semiconductor devices, it is known to form passivation films on device surfaces to improve and stabilize their characteristics, to suppress long term variations and to achieve high reliability. To form such passivation films and to protect the semiconductor devices from external contamination, various techniques are used. In order to prevent metal electrodes and metal interconnects formed on semiconductor substrates from being corroded by moisture or other matter entering from the outside, it is known to form a passivation film of phosphosilicate glass (PSG) or the like to prevent intrusion of moisture after the interconnects or electrodes have been formed.
In known devices of this type, leakage paths may appear, and will cause difficulties the semiconductor device is placed into operation or after it has been in operation for a long time. In particular, after a semiconductor device has been used for a long term, thermal distortion takes place. Also, when a semiconductor device is mounted, stresses occur. In these and other cases, a gap can appear between the passivation film and the molding resin in which the device is encapsulated. Moisture enters the gap, thus creating a current leakage path.
FIGS. 3 and 4 show a semiconductor device according to the prior art having components formed on a chip 10 which is composed of a substrate 1 cut from a wafer along scribe lines 7. The device includes a passivation film 3 which, in the completed device, will be covered by a layer or body of molded resin (not shown). For reasons outlined above, a gap may appear between film 3 and the molded resin and it has been found that leakage paths 13 are often produced by moisture or mobile ions permeating any contaminant that fills in the gap at the interface between passivation film (or overcoat film) 3 formed on the semiconductor device, or chip, 10 and the molded resin formed on passivation film 3. The aforementioned gap is quite narrow and easily formed by thermal distortion produced during operation of the chip or by stress produced during installation. More specifically, in this case, the electrode plate 6 or the metal forming a bump 5 of an electrode 4 which is at a higher potential than one chip edge 7 is ionized. The resultant ions move toward the chip edge 7 that is at a lower potential.
It is considered that leakage paths 13 are formed between the electrodes 4 at the higher potential and the chip edge 7 at the lower potential or between electrodes 4 at higher potential and electrodes 4 at lower potential. Such leakage paths 13 are frequently produced in the electrodes to which high voltages are applied and between power supply electrodes conducting high electric current densities. Leakage paths 13 deteriorate the characteristics of IC chip 10 and induce malfunctions. Electric currents flowing through the leakage paths erode the electrodes 4 and other components, thus impairing the long-term reliability of the device. Especially, progress of corrosion of electrodes of aluminum is a well-known problem and opens the bonded part.